This invention pertains to control circuits for stepper motors.
This invention is in the same field as that set forth in U.S. Pat. No. 3,767,993, patented Oct. 23, 1973 by the same inventor. The present circuitry and the mode of operation are; however, clearly different from those of the patent. In the patent, damping was accomplished by momentarily energizing all of the typically three phases of the stepper motor.
The art has employed so-called "retrotorque" pulses, these being briefly applied to a phase of a plural phase stepping motor, that phase being the phase just previously energized. This manner of achieving critial damping has been stated as effective with any number of phases, but has typically been employed with three phase stepping motors. A ring counter is used to provide bi-directional driving pulses for the plural phase motor from a single train of incoming drive pulses, and time delay means are employed for achieving appropriate timing of the retrotorque pulse.
The art has also employed means for applying a braking pulse to a phase winding that had just been previously energized, but has required auxiliary pole pieces and windings on the stepping motor.
The art has also employed the method of accelerating the rotor in the desired direction with a known power pulse, subsequently decelerating it with a retropulse applied to another winding, and then allowing re-acceleration by terminating the retropulse.